Telephone system



Oct. 22, 1940. p MAHONEY ET AL 2,218,850

TELEPHONE SYSTEM Filed March 16, 1938 5 Sheets-Sheet l SELECTOR SELECTORswncn INVENTORSv HARRY P. MAHONEY CLARENCE E. LOMAX ATTORNEYS Oct. 22,1940.

H. P. MAHONEY ET AL TELEPHONE SYSTEM Filed March 16, 1938 5 Sheets-Sheet3 5.2% SE mam Emu r HARRY F! MAHONE'Y BY CLARENCE E.LOMAX M, 1du 7INVENTORS.

I ATTORNEYS.

1940. H. P. MAHONEY' ET AL 2,218,850

TELEPHONE SYSTEM Filed March 16, 1958 5 Sheets-Sheet 5 m .sEE: @5252 NSa3 is EN.) h @mw QM mm? is -3 m mg mN L Q6 NE 80$ M00 QM.

w E m N3 6? al j 68 BY. I

ATTORNEYS.

Patented Oct. 22, 1940 TELEPHONE SYSTEM Harry Paul Mahoney and ClarenceErnest Lomax, Oak Park, Ill., assignors to Associated ElectricLaboratories, Inc., Chicago, 111., a corporation of Delaware ApplicationMarch 16,

62 Claims.

The present invention relates to improvements in telephone systems andhas iorone of'its objects the provision of improved apparatus forterminatinganultiparty rural subscribers lines in a telephone exchangewhich utilizes automatic switching equipment for setting upconnectionsbetween the various lines of the system.

In the usual arrangement 01' existing installed automatic exchanges,wherein certainoi the lines 0 extending to the exchange are of the ruralmultiparty type and others are of the single party type, nodifferentiation is made between the lines as regards the mode ofterminating the lines in the automatic switching equipment. As a re- 15suit, the initiation of a reverting call on one of the rural linesusually results in the seizure of certain of the regular automaticswitching equipment provided in the terminating exchange. Moreparticularly, when a reverting call is ini- 20 tiated on a rural line,one of the non-numerical automatic switches provided in the exchange isassigned to the use of the line having the calling condition createdthereon and operates to switch the calling line through to one, of thenumerical 2.1 impulse responsive switches. In certain instances, thes'eized switches are held operated for the duration of .the revertingcall. In other systems, apparatus is provided-for causing the release ofthe operated switches after a prede- 30 termined time interval haselapsed following the seizure of the switches. In either case, certainof the regular automatic switching equipment is tied up so that it cannot be used by the other lines.

'35 It is a further object of the present invention,

therefore, to provide in an automatic telephone system apparatus forpreventing any of the regular switching equipment provided in anautomatic exchange from. being taken for use by a m line having accessto the equipment when a reverting call is initiated on the line.

More specifically, it is an object of the invention to provide in anautomatic telephone system an improved arrangement wherein the regular4,5 automatic switching equipment is only rendered 1938, Serial No.196,136

efliciency of the line is found to be extremely poor.

It is an additional object of the invention to provide, in conjunctionwith the regular automatic switchingequipment of an automatic exchange,improved apparatus for controlling the selective signalling'of thesubstations associated with a multiparty line terminating at theswitching equipment having access to the line.

It is. another object of the invention to provide an improvedarrangement for guarding the multiparty lines against seizure by theautomatic switching equipment having access thereto during intervalswhen the rural lines are occupied with reverting calls.

In the illustrated embodiment of the invention, the multiparty ruralsubscribers lines extending to the exchange are terminated at a group ofimproved numerical or connector switches by way of which connections arerouted from the single party lines of the system to the rural lines. Therural lines are also terminated in the bank contacts of a group ofauxiliary automatic switches which function to render the regularautomatic switching equipment provided in the exchange connected by wayof trunk lines to certain of the non-numerical switches located in theexchange. Allotter means are provided in association with the severalfinder-repeater links for the purpose of assigning these links tosuccessive calling ones of the rural subscribers lines in a definiteorder. '33 Individually provided at the respective substationsassociated with the respective rural lines are manually operable magnetogenerators which are used for signalling between the substations of thelines on reverting calls. The arrange- '0 ment is such that an idle oneof the finder-repeater links is assigned to the use of any line when-acall is initiated on the line through the operation of one of thegenerators provided at one of the substations associated therewith. The

seizure of a finder-repeater link does not, :however, result in theseizure of any of the regular automatic switching equipment, each linkbeing so arranged that it functions to switch the connection through toone of the numerical switches only in response to the transmission of apredetermined series of impulses thereto by way of the callingsubscriber's line or, in other words, in response to a predeterminedoperation of the impulsing device provided'at the calling substationassociated with the calling line. .More specifically, there is providedin each link an impulse responsive relay which is adapted to beconnected to respond to impulses transmitted by way of a seized callingline and in cooperation with the associated control apparatus functionsto condition certain of the automatic switching equipment to respond tofurther operation of the impulsing relay. This control apparatus is soarranged that an artificial leak impedance is connected across thecalling line during the dialing of the preliminary digit, whereby thesensitivity of the impulsing relay is reduced during the transmission ofthe first impulse series and this relay is tested to determine itsresponsiveness to the transmitted impulses. In the event it is foundthat the impulsing relay is not faithfully responsive to the impulses ofthe first series, the control apparatus functions to prevent any of theautomatic switching equipment from responding to further operation ofthe impulsing relay. If, however, the impulsing relay is faithfullyresponsive to the impulses of the first series, the control apparatusoperates to disconnect the artificial leak impedance from the callingline to enhance the responsiveness of the impulsing relay to furtherimpulses transmitted over the calling line.

A timing device is provided in common association with the severalfinder-repeater links and, if a call initiated on a rural line happensto be of a reverting nature, this device functions to cause the seizedone of the finder-repeater links to be released a predetermined timeinterval after it is seized. Each link is provided with controlapparatus for marking any associated calling line as busy, thereby toprevent its seizure by one of the numerical or special connectorswitches. When any link is released through the operation of the timingdevice, the above-mentioned control apparatus functions toremove thebusy marking and to substitute therefor a marking identifying theassociated line as idle. This apparatus further functions to signal overthe calling line that the line is no longer guarded against seizure byone of the connector switches.

In accordance with a further feature of the invention, each of theimproved connector or final selector switches at which the rural linesterminate is provided with two operating positions for each of thelines. There is provided in common association with this group ofconnector switches ringing apparatus which comprises a plurality ofringing current conductors and 9. cyclically operating interrupterswitch of improved arrangement for impressing on the ringing currentconductors the voltage of the ringing current source for coded intervalswhich are different for each of the conductors. The arrangement is suchthat, when any one of the connector switches is operated to one of thetwo positions corresponding to a particular line, one particular ringingcurrent conductor is connected to project ringing current over the lineand, when the switch is operated to the other of the two positionscorresponding to the line, a second ringing current conductor isconnected to project ringing current over the line. Further inaccordance with this feature of the invention, the control apparatusprovided in each of the connector switches is arranged automatically todiscontinue the application of ringing current to a selected line afterthe current has been applied to the line for a predetermined number ofringing cycles. More specifically, the cyclically operating interrupteracraaao switch is arranged to apply to a control conductor extendingtherefrom a predetermined potential at the beginning of each cycle ofits operation, and a plurality of relays are provided in each connectorswitch which are so connected and arranged as sequentially to operate inresponse to successive applications of the said predetermined potentialto the control conductor. The first of these relays to operate functionsto connect the particular selected ringing current conductor to theselected line, and the last of the relays to operate functions todisconnect the ringing current conductor from the selected line and toconnect the trunk line incoming to the connector switch to thesubscriber's line.

Further features of the invention pertain to the particular arrangementof the circuit elements whereby the above and additional operatingfeatures are obtained.

The novel features believed to be characteristic of the invention areset forth with particularity inthe appended claims. The invention, bothas to its organization and method of operation, together with furtherobjects and advantages thereof, will best be understood by reference tothe specification taken in connection with the accompanying drawings inwhich Figures 1 to 5, inclusive, illustrate an automatic telephonesystem having incorporated therein the features of the present inventionas briefly outlined above.

Referring now to the drawings, the system there illustrated comprises,in general, an exchange, a plurality of single party subscribers lines,two of which are illustrated at "I and I04, extending to the exchange,and a plurality of subscriber-controlled automatic switches including aline switch I00, two selector switches I20 and I40, and a connectorswitch I50 for setting up connections between the various subscriberslines. Also extending to the exchange are a group of rural subscriberslines, one of which is illustrated at 600, each of which is of themultiparty type. The rural lines are terminated in the bank con tacts ofa'group of special connector switches, one of which is illustrated inFig. 2, and also in the finder portions of a group of finder-repeaterlinks, one of which is shown in Fig. 4. Each repeat-er is connected byway of a trunk line to a line switch and is operative to render theregular automatic switching equipment accessible to the rural lines.Thus, the repeater illustrated in Fig. 4 is connected by a trunk lineI25 to a line switch I30 which has access to certain of the selectorswitches in the exchange. For the purposeof assigning thefinder-repeater links to successive calling ones of the ruralsubscribers lines in a definite order, there is provided in associationwith these links an allotter switch forming a part of the commonequipment indicated generally at 500. The special connector switches ofthe group having access to the rural lines have associated'therewithringing apparatus as illustrated in Fig.3, which functions in a mannersuch that selective code ringing of any desired substation on a selectedrural line may be achieved. It is pointed out that the line switches I00and I30 and the other similar switches corresponding thereto arenon-numerical switches in the sense 2,a1e,aco. I a 3 form particularline selecting functions ,in response to impulses transmitted thereto.'It will maximum volume of trafllc the particular switch group isrequired to handle. Further in accordance with conventional practice,each 0! thesingle party subscribers lines is multiplied to thecorrespdnding'bank contacts of a group.

of connector switches, whereby a plurality of switches are available forsetting up connections between each line and any other line of thesystem., The line switches, on the other hand, are individuallyassociated with the respective subscribers' lines, that terminating theline IOI being indicated at I00.

The end of each subscriber's line remote fromthe exchange terminates inone or more subscribers substations, the arrangements of which aredifferent depending upon whether the line is of the single party type oris one oi! the group of mutiparty rural lines. Two substations of theusual automatic type are diagrammatically illustrated at A and B inassociation with the lines I M and I04, respectively. In brief, each oi!the single party line substations may comprise the usual hand set typeof transmitter and receiver, acradle or hook switch, a ringer, and animpulsing device for transmitting the switch control impulses by way ofthe associated line to the automatic switching equipment located in theterminating exchange. These substations are of the well-known commonbattery type. The substations associated with the respective rurallines, on the other hand, are of the local battery type,

,one such substation being illustrated in detail at E in Fig. 5 and twoother substations of similar type being diagrammatically illustrated atC and D, respectively.

Each of the line switches I00, I30, etc., is preferably of thewell-known rotary type, of which there are several commercialembodiments Each wipers thereof to a position opposite a particularlevel of bank contacts and then rotated to bring the wipers intoengagement witha particular set of contacts in a selected level;vertical, rotary and release magnets; and control relays suitablyconnected and arranged to control the energization of the variousmagnets and the line switching in accordance with theparticularfunctions of the particular switch. In all fundamentalrespects, these switches are similar to the connector switch illustratedin detail in Fig. 2. Obviously, the particular arrangement of thecontrol apparatus embodied in the switches of different type isdiflerent in each instance, 'depending upon the character 'of'theswitch.

Neglecting for the present the details of the apparatus terminating themultiparty rural subscribers line, the system as described above is,

in general, entirely conventional in form and its operation is wellunderstood in the art. In brief,

' when a subscriber, such, for example, as the subscriber at .thetelephone A, initiates a call over the line IN to a second subscriberstelephone, such, for example, as the telephone at the station B, bylifting his receiver from its hook, a loop circuit is completed by wayof the line IOI for initiating the operation of the line. switch mtoselect a trunk line leading to an idle selector switch. Assuming, forexample, that the selector switch I20 is the first numerical switchselected for the use of the calling line IOI, when the trunkline-leading to this selector switch is found, the loop circuit isextended to this switch and? the switch is conditioned to respond'to thefirst series of impulses dialed at the calling substation. With theselector switch I20 in this condition, dial tone is returned over theestablished loop to the calling subscriber to indicate that the dialingoperation may be started. When the first digit is dialed at the callingsubstation, the switch I20 elevates its wipers to a position oppositethe level of bank contacts terminating the trunk lines respectivelyextending to the connector switches having access to the called lineI04. Followingvthis operation, the wipers of the switch I20 areautomatically stepped over the contacts of the selected level until atrunk line leading to an idle connector switch of the selected group isfound. Assuming that the connector switch I is the first idle connectorswitch available, when the wipers of the switch I20 are stepped intoengagement with the contacts terminating the trunk line extending tothis connector switch, the subscribers loop circuit is extended thereto,thereby to cause this connector switch to be con-' ditioned to respondto the second and third series of impulses dialed at the callingsubstation. In response to the dialing of the second digit, the wipersof the connector switch I50 are stepped verticallyto a position oppositethe level of bank contacts at which are terminated the lines of theten-line subgroup including the called line I04. Following this seriesof impulses, the connector switch is conditioned to rotate its wipersstepby-step in accordance with the impulses making up the third andfinal digit dialed at the calling substation. When the last digit isdialed, the wipers oi the switch I50 are stepped into engagement withthe set of bank contacts terminating the called line I04. In accordancewith conventional practice, suitable provisions are made in theconnector switch I50 for testing the called line to determine its idleor busy condition, for returning busy tone ,over the established-loop tothe calling subscriber in case the called line is busy and for applyingringing current to the called line inthe event this line is idle at thetime it is selected. Assuming that the line I04 is idle, the desiredconversational connection is completed when the called substation B isanswered. Also in accordance with conventional practice, the apparatusis arranged to insure its release when the connection is cleared out atthe calling and called substations. Any desired mode of initiating therelease of the established switch train may be utilized. For example,the control apparatus embodied in the connector switch I50 may be soarranged thatthe release of the connection is entirely under the controlof the calling party. Alternatively, the apparatus may be so arrangedthat the release of the connection is under the control of the lastparty to hang up.

As indicated above, each of the substations associated with the ruralsubscribers lines is of the local battery type. More particularly, thesubstation E illustrated in Fig. 5 comprises a transmitter 8 which isarranged to be connected in a closed circuit including the primarywinding ii I of a .transformer H and a local battery 0l3 through theoperation of a hook switch 620. The substation equipment furthercomprises a receiver 6I5, an impulsing device 630, an alternatingcurrent generator 6050f the magneto type, and a signal device in theform of a ringer 603 which is normally connected across the conductorsof the line 600 over a path including a condenser 504 and certain of thesprings embodied in the hook switch 620. It will be understood that themagneto or alternating current generators individually provided at thesubstations associated with the line 600 comprise means for signallingbetween the substations on this line on reverting calls.

Referring now more particularly to the finderrepeater links by way ofwhich connections are routed from the rural subscribers linesv to theregular automatic switching equipment and considering the linkillustrated in Fig. 4 as exemplary, this link comprises a finder switch490 of the wellknown rotary type. In brief, the finder switch comprisesfour sets of bank contacts 4! to 494, inclusive, wipers 495 to 498,inclusive, individually associated with the respective bank contactsets, a motor magnet 499 for driving the wipers over the contacts oftheir respective associated sets, and a switching-through relay R4) forconnecting any selected calling line through to the repeater portion ofthe link.

For the purpose of assigning idle ones of the finder-repeater links tothe various successive calling ones of the rural lines in a definiteorder and for the further purpose of controlling the operation of aselected finder switch to search for and seize a calling line, there isprovided in association with the finder-repeater links the commonequipment 500. This common equipment includes a rotary link allotterswitch having five sets of bank contacts to 505, inclusive, wipers 505to 5l0, inclusive, respectively associated with thebank contact sets, amotor magnet 5H for driving the enumerated wipers over the contacts oftheir associated sets, a start relay R520, and three relays R530, R540and R550 for controlling the operation of the rotary switch to find anidle link and for controlling the operation of the finder portion of aselected link to find a calling line.

In order to initiate the operation of the common equipment 500. when acalling condition is created on one of the rural subscribers lines, eachline has individually associated therewith an alternating current relaywhich is operative in response to the operation of any one of themagneto generators provided at the substations on the associated line.Such a relay is indicated at R405 as including a winding normallyconnected across the line conductors of the line 500. In order toprevent the operation of this relay when the associated line is seizedby one of the special connector switches, a cut-off relay R400 isprovided which operates to disconnect the upper or alternating currentwinding of R405 from across the conductors of the line 500 in responseto the seizure of the line 600 by any one of the connector switches.

The repeater portion'of the link illustrated in Fig. 4 comprises arepeating coil 412, a line or ,impulse repsonsive relay R4I5, aslow-to-release hold relay R430, an impulse correcting network and aswitching-through relay R460 which is under the control of an impulseresponsive switch 480-. The relay R450 is a pulsing relay which respondsto the operation of R! and functions to'repeat impulses to the switch480 and to the automatic switches constituting the regular automaticswitching equipment. The switch 480 is of the well-known minor type andcomprises two sets of bank contacts 48! and 482, wipers 483 and 484respectively associated with the contact sets 48l and 482, an operatingmagnet 485 for driving the wipers 483 and 484 over the contacts of theirrespective associated sets, a release magnet 481, and off-normal springs486 for controlling the energization of the release magnet. There arealso provided in the repeater portion of the link two relays R410 andR415 which function to control the operation of the switch 480.

For the purpose of releasing the link a predetermined time intervalafter it has been assigned to the use of a line having a reverting callinitiated thereon, there are provided three additional relays R560, R510and R500, the last two of which are under the control of a pulsegenerator 515. The relay R560 also functions as a device for marking thelink illustrated as busy in the bank contacts of the allotter switch andas a hold relay for maintaining the link operated following theextension of a subscribers loop circuit to the repeater portion thereof.The pulse generator 515 may be of any well-known construction whichincludes means for alternately applying ground pulses to the time pulseleads C551 and C513 at spaced intervals. If desired, it may comprise acommutator driven by a synchronous motor through a speed reducingmechanism and including grounded commutator segments suitably arrangedto engage brushes respectively terminating the leads C551 and C513.

Referring now more particularly to the group of improved connectorswitches by way of which the regular automatic subscribers lines gainaccess to the rural lines, it is pointed out that the connector switchesof this group may be of identical construction and arrangement. For thisreason, only the switch illustrated in Fig. 2 will be described indetail, but it will be understood that each of the rural lines ismultipled to the corresponding bank contacts of each of the switches ofthis group. In brief, the switch shown in Fig. 2 comprises a switchingmechanism 244, of the Strowger type, which includes a plurality of bankcontacts arranged in levels; wipers for engaging the contacts; meanscomprising a vertical magnet 291 and a ratchet and pawl mechanism, notshown, for translating the wipers to a position opposite a; desiredcontact level; means comprising a rotary magnet 295 and a ratchet andpawl mechanism, not shown, for thereafter rotating the wipers step bystep into engagement with a selected contact set in the selected level;a release magnet 239 for causing the wiper oarriage structure to bereturned to normal during the release of the switch, vertical ofi-normalsprings 265 and a plurality of control relays for controlling theoperation of, the three enumerated magnets and the auxiliary functionsof the switch. Of these relays, R200 is the usual line or impulsingrelay, R204-is the usual hold relay and is of the slow-to-release type,R2 [0 and R220 are slow-to-release pulse circuit control relays, R230 isa ringing control relay, and R2 is the busy test relay. The-remainingrelays illustrated in Fig. 2, namely, R240, R250, R260 and R210, areprovided in accordance with one feature of the present invention forcontrolling the ring cut-oi! operation and the line switching operationin an improved manner. For the purpose of selectively signalling thevarious substations associated with 7 the rural subscribers lines, codedringing is utilized. To this end, the code selecting switch 280 isprovided in the connector switch and is arranged to respond to impulsestransmitted thereto by way of a calling line. This code selector switchis of the well-known minor type and comprises two sets of bank contacts28I and 232 tions between the regular automatic subscribers lines, thereis provided'a repeater 290 which is inserted in and divides into twosections the trunk line incoming to the connector switch illustrated inFig. 2.

The ringing current conductors terminated at the bank contacts of thecode selector switch 280 form a cable 3" extending to the bank contactsof an interrupter switch 300, illustrated in Fig. 3.

- and comprises a plurality of sets of bank contacts 382 to 392,inclusive, wipers 310 to 380, inclusive, respectively associated withthe bank contact sets, and means comprising an operating magnet 365 anda ratchet and pawl mechanism, not shown, for driving the enumeratedwipers over the contacts of their respective associated contact sets.This switch functions to impress on the respective ringing currentconductors the voltage of an alternating current source 325 forpredetermined intervals during each cycle of its operation, and the bankwiring of the switch is such that the, coded voltage impressed on eachconductor during eash ringing cycle is different in character from thatimpressed on each of the other ringing current conductors. Moreparticularly, the voltage of the source 325 is impressed on each of theenumerated wipers ofthe interrupter switch by way of a transformer 326having a primary winding 32! connected across the source and a secondarywinding 328 having one terminal grounded and the opposite terminalarranged to be connected to the respective wipers. The contact bank ofthe switch 300 is wired in an improved manner, described moreparticularly hereinafter, such that the coding of the ringing voltageapplied to the several ringing current conductors is difierent foreachconductor. For the purpose of controlling the operation of theinterrupter switch there is provided in association therewith a startrelay R3I0 and a group of cyclically operating slow-to-operate relaysR320, R330 and R340. Specifically, this group of relays functions toconnect the wipers of the interrupter switch to the winding 328 and toenergize the operating magnet 365 once during each cycle of theiroperation.

Operation of the ringing interrupter The operation of the ringinginterrupter is initiated when ground is applied to the start conductorC3I B by one of the special connector switches in the group includingthe switch shown in Fig. 2, to complete an obvious circuit forenergizing the start relay R3 I 0. The relay R3 I 0, upon operating,completes, at RA3I3, a path for applying a predetermined potential,namely, ground potential, to the pick-up or control conductor C3I5. AtRA3I2, the relay R3I0 prepares a, circuit, traced hereinafter, formaintaining itself energized independently of its operating circuit astraced above and until the interrupter switch has been operated througha complete cycle. The relay R3 I 0 also'completes a circuit forenergizing the slow-to-operate relay R320, this circuit extending fromground at RA3I I by way of the winding of R320 and. the resistor 3| 4:tobattery.

,The relay R3 0 operates, after an interval, to open, at RA32I, a pointin the path normally short-circuiting the winding of R330, permittingthe latter relay to be energized over a circuit extending from ground atRA3II by way of 'the winding of R330 and the resistor 320 to battery.

The slow-to-opera-te relay R330 operates, after an interval, to open, atRA33I, a point in the path normally short-circuiting the winding ofR340,

permitting this latter relay to be energized over a circuit extendingfrom ground at RA3I I by way of the winding of R340 and the resistor 343to battery. The slow-to-operate relay R340, in

turn, operates, after an interval, to complete, at

RA342, an obvious path for 'short-circuiting the energized winding ofR320, causing the last-mentioned relay to restore. When R320 restores,it

completes, at RA32 I, the path for short-circuiting.

the winding of R330. The relay R330 now restores to complete, at RA33I,the above-mentioned path for short-circuiting the winding of R340. WhenR340 restores, it opens, at RA342,

the path short-circuiting the winding of R320, permitting this latterrelay to again be energized over its operating circuit as traced above.Thus, a second cycle of operation of the three relays R320, R330 andR340 is initiated. During each operating cycle of these three relays, acircuit is completed for energizing the operating magnet 365 embodied inthe interrupter switch 300. Thus, when R340 operates, it completes, atRA34I, an obvious circuit for energizing the magnet 365. Assuming thewipers of the switch to be standing in the home position as shown in thedrawings, when this magnet is energized, the magnet, in cooperation withits associated ratchet and pawl mechanism, not shown, operates to stepthe wipers with their respective associated second contacts. It ismanifest that, for each succeeding cycle of operation of the threerelays R320, R330 and R340, the magnet 365 is energized to cause theenumerated wipers to be moved another step. As

/ pointed out immediately hereinafter, movement of the enumerated wipersover the contacts of their respective associated sets results in thecoding of the ringing voltage applied to the various ringing currentconductors terminating in the bank contacts of the code selector switch200.

-This is by virtue of the particular bank wiring 310 to 380, inclusive,one step or into engagement and with difierent spacing intervalstherebetween. Thus, as the wiper 310 travels over the first twelvecontacts of the set 382, it is connected to the ringing currentconductor 32 while standin in engagement with its associated second,third, fourth, sixth and seventh contacts. While in engagement with eachof these contacts, the voltage developed across the transformer 328 isimpressed on the conductor 32 for a short interval. Thus, with the wiper310 standing in engagement with its second contact and when R330operates during the second cycle of operation of the three relays R320,R330 and R340, a path is completed for connecting the upper terminal ofthe secondary winding 328 to the jumper connection 388', this pathextending by way of R0333 and RA332. The jumper connection noted ismultiplied between the wipers 310 to 313, inclusive, and between thewipers 318 to 380, inclusive. Hence,

the voltage developed across the secondary winding 328 is 'impressedonany ones of the ringing current conductors which extend to therespective second contacts associated with the enumerated wipers. Sincethe second contact of the set 382 is connected to the ringing currentconductor 32, this conductor has impressed thereon the voltage of theringing current source when R330 operates. Similarly, the ringingcurrent conductors 3|, 4, 34, 4|, 44., l and 43 have the voltage of thesource impressed thereon with the wipers of the interrupter switchstanding in the position noted. When R340 operates, following theoperation of R330.in the second cycle of operation of the three relaysnoted, the

magnet 385 is energized to advance the wipers into engagement with theirrespective associated third contacts. This movement of the wipers,however, does not result in the disconnection of the ringing currentconductors from the upper terminal of the secondary winding 328 for thereason that each of the wipers is of the bridging type arranged tobridge two contacts during the transition interval when it is beingmoved from one contact to another. When R340 operates, however, itcauses the rapid sequential restoration of R320 and R330 in the mannerpointed out of operation of these relays, the potential of the source isimpressed on those of the conductors connected to the fourth contacts ofthe sets respectively associated with the enumerated wipers, and so on.It will be noticed from an inspection of the drawings that the ringingcurrent conductor 32, for example, is not connected tothe fifth contactof the set 382. Hence, during the cycle of operation of the three relaysR320, R330 and R340 to advance the wipers from engagement with theirrespective associated fifth contacts and into engagement with theirrespective associated sixth contacts, the potential of the ringingcurrent source is not impressed on this particular ringing currentconductor. A spacing interval is, therefore, provided between the firsthalf of the code and the second half. Since the conductor noted,

namely, the conductor 32, is connected to the sixth and seventh contactsofthe set 382, this second half of the code cycle comprises twoadditional short ringing periods. From this point on and until thewiper-310 is advanced into engagement with the fifteenth contact of theset 382, the conductor 32 is held disconnected from the rin ing currentsource.

The arrangement is such that two ringing cycles are completed duringmovement of the switch wipers over the twenty-five points of the switch.The end of the first cycle is reached when the wipers are advanced intoengagement with their respective associated thirteenth contacts, and thewipers are moved to a position to begin the second ringing cycle whenthey are driven into engagement with their respective associatedfourteenth contacts. In order to render the spacing between cyclessubstantially equal, it is desirable rapidly to move the wipers fromengagement with their respective associated thirteenth contacts and intoengagement with their respective associated fourteenth contacts. To thisend, the thirteenth contact of the set 388 is included in a circuit forenergizing the magnet 385 by way of the self-interrupting contactsassociated with the armature 388, this circuit being completed when thewiper 314 is advanced into engagement with the thirteenth contact of theset 388 and extending from ground on this wiper by way of C338, thearmature 388 and the winding of the magnet 385 to battery. Whenenergized over the above-traced circuit, the magnet 385 operatesimmediately to advance the wipers into engagement with their respectiveassociated fourteenth contacts independently of the cyclically operatingrelays R320, R330 and R340. This operation marks the-beginning of thesecond ringing cycle. During this second cycle, the voltage of theringing current source is impressed on the various ringing currentconductors for coded intervals which are identical with those producedduring the first ringing cycle. Thus, during the respective intervalswhen the wiper 310 is standing in engagement with the fifteenth,sixteenth, seventeenth, nineteenth and twentieth contacts of the set382, the voltage of the source is impressed on the conductor 32 throughthe operation of the relay R330. During the interval when this wiperstands in engagement with the eighteenth contact of the set 382, theconductor 32 is held disconnected from the source so that a spacinginterval is provided which corresponds to that produced when the wiperis moved into engagement with its fifth contact. When the wiper 310 ismoved from' engagement with the twentieth contact of the set 382, thevoltage of the source is held disconnected from the ringing currentconductor 32 until this wiper is again moved into engagement with thesecond contact of the set 382 at the beginning of the third ringingcycle.

As indicated above, the coding of the voltage applied to each of theringing current conductors during each ringing cycle is different ineach instance. Thus, considering the ringing current conductor l3, forexample, this conductor has applied thereto the voltage of the sourcefor a short interval, followed by three narrowly spaced short intervalswhich are relatively widelyspaced from the first interval, during eachringing cycle. More particularly, when the wiper 3 is moved intoengagement with the seventh contact of the set 383 and when R330operates, the conductor [3 is connected to the ringing current source.

Thereafter and during the interval when the,

wiper "I is standing in engagement with the eighth contact of the set303, the conductor I3 is held disconnected from the source. When,however, the wiper 310 is moved into engagement with the ninth contact'of the set 302, this conductor is connected to the source by way of theWiper 310. Thereafter, and during the intervals when the wiper 31! isstanding in engagement with the tenth and eleventh contacts of the set383, the conductor 13 is connected to the source for short intervalsmeasured by the time required for R330 to operate and restore. Byinspection of the bank contact wiring arrangement, it will be apparentthat the same coding of the voltage applied to the conductor 13 occursduring the second ringing cycle or duringthe movement of the wipers overthe contacts numbered from IE to 25, inclusive.

It is believed that the mode of applying the voltage of the ringingcurrent source on the remaining ringing current conductors willbeapparent from the wiring arrangement illustrated in the drawingsconsidered in light of the preceding description pertaining to the twoconductors 32 and I3. It is pointed out, however, that the numberidentifying each of the ringing current conductors is indicative of theparticular coding of the voltage impressed, respectively, thereon. Moreparticularly, during each ringing cycle, the conductor l2 has impressedthereon the voltage of the source for one short interval, followed by aspacing interval which is succeeded by two successive and closely spacedshort ringing intervals.

Similarly, the conductor 34 has impressed beginning of each ringingcycle. Thus, if the ringing apparatus is started with the interrupterswitch standing in the position shown in the drawings, the path forapplying ground potential to the conductor noted is completed when R3|0operates. This circuit extends from ground as applied to the wiper 315by way of the first contact of the set 381 and RA3I3 to C3l5. Again,when the wipers are driven over their associated contacts to a positionwhere the wiper 315 engages the fourteenth contact of the set 381, thispath is again completed. As the switch continues to operate, this pathis completed for a short interval at the beginning of each ringingcycle.

The arrangement of the coding switch and its associated apparatus issuch that the operation thereof continues until a ringing cycle whichhas been started is completed, irrespective of whether the operatingcircuit for the start relay R3I0 is maintained completed. To this end,an alternative circuit is provided for maintaining the start relay R310energized independently of its operating circuit. This hold circuit forR3l0 is prepared, at RA3I2, when R3l0 operates, is completed when thewiper 314 is moved into engagement with the second contact of the set386, and is held completed until this wiper is moved into engagementwith the thirteenth contact of the set 386. Hence, when the firstringing cycle is started, R3I0 is held operated until the cycleis'completed. Again, when the wiper 314 is moved into engagement withthe fifteenth contact of the set 386 to initiate the second ringingcycle, this holding circuit is again completed and is held completeduntil the wiper noted'is again moved into engagement with the firstcontact of the set 386. By virtue of this arrangement, it is notpossible for improperly coded ringing current to be projected over aselected subscriber's line.

The release of the ringing interrupter is brought about by the removalof ground potential Operation of the apparatus to extend a. connectionto a rural'subscribers substation Referring now more particularly to theopera tion of the apparatus to extend a connection from one of theregular automatic subscriber's lines, such, for example, as the-line IN,to one of the's'ubstations associated with the line 600,' and assumingthat the line switch I00 opcrates to extend the connection from thecalling substation A to the selector switch i 20, when a predetermineddigit is dialed at this substation, the selector switch noted is causedto operate automatically to select an idle one of the special connectorswitches in the group including the switch illustrated in Fig. 2.Assuming the switch illustrated is the first available idle switch ofthe selected group, when the subscribers loop circuit is extended by,way of the trunk line l2l to this connector switch, the line relay R200operates to complete, at RAI and R0202, an obvious circuit forenergizing the slow-to-release hold relay R204. The hold relay, uponoperating,.removes, at RA205 and R0206, battery potential, as extendedby way of the resistor 221 to RC206, from the control conductor CI ofthe trunk line I2]. At RA205 and R0206, groundis applied over an obviouspath to the control conductor noted. Throughthe removal of batterypotential from.Cl24 and the substitution of ground potential, theconnector switch illustrated is marked as busy, thereby to prevent itsseizure by another of the selector switches on another call to one ofthe rural lines. At RA208 and RC209, the

relay R24 prepares a point in the pulsing circuit, traced hereinafter,for energizing the slowto-release relay R2 l0 and the vertical magnet291 in series. This circuit is completed, when R200 restores at thebeginning of the first impulse of the second digit dialed at the callingsubstation A and extends from ground at RA20| by way of R0203, RA208,R0209, the oil-normal springs 269 and 2 68,.the winding of R2l0, thecontact springs 298, and through the winding of the magnet 291 tobattery. Upon being energized over the abovetraced circuit, the magnet291. attracts its associated operating armature to step the wipersembodied in the switching mechanism 2 one step vertically or to aposition opposite the first level of bank contacts. During this firststep taken by the wipers; the oiT-normal springs 265 are moved to' theoff-normal position to interrupt, at the springs 268 and 269, theabove-traced impulsing circuit and to prepare, at the springs 269 and263', an alternative impulsing circuit. This latter circuit is completedupon the operation of R2l0, which occurs simultaneously with theoperation of the magnet 291. At the springs 261 ground is applied to theringing interrupter start conductor 0M6, thereby to initiate theoperation of the ringing interrupter in the manner pointed out above. Atthe beginning of the sec- 0nd impulse dialed at the calling substationA, the above noted alternative impulsing circuit is completed.Specifically, this circuit extends from ground at RA20| by way of R0203,RA208, R0209, the off-normal springs 259 and 269', RA2I I, R02l3, thewinding of R210, the springs 298 and through the winding of the magnet291 to battery. When energized over the above-traced circuit, the magnet291 again attracts its associated operating armature to cause the wipersof the mechanism 2 to be stepped a second step vertically or to aposition opposite the second level of bank contacts. Thereafter, themagnet 291 is energized once for each impulse of the second digit dialedat the calling substation so that, at the conclusion of this digit, theswitch wipers embodied in the mechanism 2 stand in a position oppositethe level of bank contacts terminating the lines of the group includingthe called line '600. During this series of impulses, the relays R204and R2l0 are held operated due to the slow-to-release characteristicsthereof. end of the second digit dialed at the calling substation, theline relay R200 isheld energized for a sufiicient time interval topermit R2l0 to restore. This relay, upon restoring, opens, at RAZI I andR02l3, a point in the alternative impulsing circuit over which R2l0 andthe magnet 291 were energized in series and prepares, at RA2|I andR0212, a circuit for energizing the slow-torelease relay R220 and therotary magnet 295 in series.

The last-mentioned circuit, namely that over which R220 and the rotarymagnet 295 are energized, is completed when the line relay R200 restoresat the beginning of the first impulse of the third digit dialed at thecalling substation. This circuit extends from ground at RA20| by way ofR0203, RA208, R0209, the oil-normal springs 269 and 269', RA2I l, R0212,RA2I5, the winding of R220, RA23I, R0232, the springs 29 6 and throughthe winding of the magnet 295 to battery. When energized over theabove-traced circuit, the magnet 295 attracts its operating armature tocause the wipers of the mechanism 244 to be stepped from vertical normalinto engagement with the first set of contacts in the selected level ofbank contacts. The relay R220, upon operating, completes, at RA22I, apath short-circuiting the armature RA2I5 of the busy relay R2l4, therebyto prevent the above-traced impulsing circuit from being opened when thewipers of the switch mechanism 244 are being moved over contact setsterminating busy lines. At RA224 and R0225, the relay R220 opens a pointin the circuit, traced hereinafter, for energizing the ringing relayR230 and, at RA224 and RA222, it prepares a test circuit, tracedhereinafter, over which the busy relay R2 may be energized. The rotarymagnet 295 is energized once during each additional impulse of the thirddigit dialed at the calling substation so that, at the conclusion of thethird digit, the wipers of the mechanism 244 are left standing inengagement with a set of contacts terminating the called line 600. Asindicated above and pointed out with greater particularity hereinafter,two operating positions are provided for At the each of the subscriberslines. Thus, 11? the wipers 245 to 240, inclusive, are stepped intoengagement with either the fifth or sixth set of bank contacts in thelevel illustrated, the connector switch will be connected to the calledline 000. Obviously, the one of these two sets selected will depend uponthe number of impulses making up the third digit. For example, if thenumber of impulses in this digit is five, the switch wipers will berotated into engagement with the contact set including the contacts 2"to 240', inclusive. 0n the other hand, if this digit comprises siximpulses, the switch wipers will be rotated into engagement with thesixth set of contacts. The particular reason {or providing twooperatihgpositions of the switch for each subscriber's line is pointedout in detail hereinafter.

with the wipers of the mechanism 2" standing in one of the two positionscorresponding to the called line 000, the succeeding operation of theapparatus depends upon. whether the called line is idle or busy. Beforedescribing the operation of the apparatus resulting when either one ofthe two conditions noted prevails, brief reference will be made to thearrangement for preventing any possibility of false operation on thepart ofthe wipers of the mechanism'fll and for preventing any noise frombeing introduced in the talking circuit extending by way of thesewipers. To this end, each of the two operating magnets 295 and 291 is soconnected and arranged that the speed of the respective associatedoperating armatures is reduced at the end of each stroke thereof andwhen they approach their respective oppositely disposed pole faces. Morespecifically, the armature controlled springs 298 associated with themagnet 291 are arranged normally to short-circuit a resistor 291' andare also arranged to be controlled by a second and relatively lightarmature, not shown,

carried by the magnet 291. This second armature is so constructed andarranged as to operate to open the springs 290 before the main operatingarmature of the magnet completes its movement. As a result, the initialenergizing path for the magnet 291 is by-passed around this resistor.When energized, however, the magnet 291 attracts the armaturecontrolling the springs 290 to open the path short-circuiting theresistor 291, thereby to reduce the energization of the magnet and causethe speed of the operating armature associated with this magnet to bereduced before the end of its stroke. Thus, the shock incident to thecompletion of the stroke of the armature is materially reduced, therebyeliminating any possibility of the wipers being falsely operated morethan one step and minimizing the vibration of these wipers. An identicalarrangement, including the contact springs 296 and the resistor 295', isprovided in association with the rotary magnet 295 for the same purpose.

Continuing now with thepperation of the apparatus which occurs followingthe selection of the called line 600, and assuming that the called lineis busy at the time it is selected, this condition is indicated by thepresence of ground potential on the control conductor 0909. When,therefore, the wiper 291 is moved into engagement with the contact 241',a circuit is completed for energizing the busy relay R2, this circuitextending from ground as applied to 0003 by way of the contact 241', thewiper 241, RA22I, RA222,RA230 and through the winding of R2! to battery.When the busy relay R2 operates, it prepares, at RA2I6 and R02|6, aholding circuit for itself, which circuit is completed upon thesubsequent restoration of the slow-to-release relay R220shortlyfollowing the end of the third digit, and extends from ground atR0206 by way of RA205, RA2I6, R02l8, R0223, RA222, RA236 and through thewinding of R2I4 to battery. At RA2I5, the busy relay opens a point inthe operating circuit for R220, thereby to prevent further impulsesdialed at the calling substation from effecting operation of R220 andthe ringing code selecting switch 280. At RA2I9, the relay R2l4, uponoperating, completes a path for conducting busy tone current by way ofthe established subscribers loop circuit through the receiver at thecalling substation. This path extends from one side of the busy tonesource as connected to 0221 by way of RA238, RA2I9, the condenser 249,one

side of the subscriber's loop circuit, the receiver at the callingsubstation, and back over the other side of the subscribers loop circuitand the upper winding of R200 to the other terminal of the busy tonecurrent source. The resulting operation of the receiver at the callingsubstation gives an audible indication identifying the called line asbusy. Following the operation of the busy relay R2l4, no furtheroperation of the apparatus occurs until the partially completedconnection is cleared out.

Upon receiving busy tone, the calling sub-'- scriber may initiate therelease of the operated switch train by restoring his receiver to itshook to cause the restoration of the line relay R200. This relay, uponfalling back, opens at RA20I and R0202, a point in the operating circuitfor the hold relay R205. When the hold relay restores, after aninterval, it removes, at RA206 and R0206, ground from the controlconductor 0124, thereby to cause the release of the selector switch I20and the line switch I00 in the usual manner. At RA205 and R0206, batteryis substituted for ground on the control conductor 0l24, to mark thetrunk line l2! as idle. The hold relay, upon restoring, also opens, atRA205 and R0206. a Point in the previously traced holding circuit forthe busy relay R2, causing this relay to restore. AtRA200 and R0201, thehold relay completes a circuit for energizing the release magnet 239,this circuit extending from ground at RA20I by way of R0203, RA208,RA201, the off-normal springs 266, and through the winding of the magnet239 to battery. The resulting operation of the release magnet causes thewiper carriage structure of the switching mechanism 244 to be restoredto vertical and horizontal normal in the usual manner. When this occurs,the oil-normal springs 265 are moved to the normal position to. open, atthe springs 266, a point in the operating circuit for the releasemagnet. At the springs 261, ground is removed from the ringinginterrupter start conductor 03l6, thereby to cause the operation of thisswitch to be arrested providing none of the other special connectorswitches associated with the interrupter switch are operated. With theapparatus in this condition, the partially established connectioniscompletely released and the switches involved therein are in readinessfor insteadof busy at the time itis selected by the connector switchshown in Fig. 2, this condition of the switch is identified by theapplication of 2,219,950 9 battery potential to the control conductor0603 thereof through the winding of R400. -When, therefore, the wiper241 is operated into engagement with the contact 241' terminating theconductor 0603, a circuit is prepared for energizing the relay R230.This circuit is completed upon the subsequent restoration of R220 andextends from ground at R0206 by way of RA205, RA2I6, R02 I 1, the lowerwinding of R230, R0225, RA224, the switch wiper 241, and the contact241' to battery as applied to 0603. The relay R230-opcrates, when itslower winding is energized over the above-traced circuit, and completes,at RA235, -a holding circuit for itself, this circuit extending fromground on R0206, by way of RA205, Cl 24, RA235 and through the upperwinding of R230 to battery. At RA234, the relay R230 applies ground tothe switch wiper 241, thereby to complete a circuit for energizing thecut-off relay R400 associated with the line 600. Specifi cally, thiscircuit extends from ground at RA234 by way of the switch wiper 241, thecontact 241', 0603, and through the winding of R400 to battery. Theapplication of ground to the control conductor 0603 of the line 600serves to mark this line as busy in the bank contacts of the variousother connector switches to which it extends. When R400 is energizedover the'circuit just traced, it opens, at RA402, a point in thecircuit, traced hereinafter, for energizing the lower winding of thealternating current relay R405, and, at RAI, it disconnects the upperwinding of this relay from across the conductors of the line 600. AtRA403, the relay R400 extends ground as applied to 0603 to theparticular bank contacts of the various finder switch contact banks,which correspond to the line 600, thereby to preclude any of theseswitches from inadvertently seizing the line 600, during the operationthereof to select another f the rural lines having a calling conditioncreated thereon.

At RA238, the relay R230, upon operating, opens a point in theabove-traced path for applying busy tone current to the loop extendingto the calling subscribers substation and, at RA231, it prepares acircuit, traced hereinafter, for energizing the first relay R250 of thegroup of ringing control relays R250, R260 and R210. At RA239, the relayR230 completes a circuit for energizing R240, this circuit extendingfrom ground as applied to the bank contact 248' by way of the switchwiper 248, RA239, and through the winding of R240 to battery. Theresulting operation of R240 to move RA24I into engagement withR0243'insures that the selected one of the ringing current conductorswill be included in the group terminating at the bank contact set 21" ofthe code selector switch 280. In this connection, it will be understoodthat, had the wipers of the mechanism 244 been operated into engagementwith the sixth set of contacts of the selected level or to the secondoperating position corresponding to the called line 600, no circuitwould have been available for energizing R240 and, hence, this relaywould not have been energized following the operation of R230. With R240deenergized, the ringing current conductor ultimately selected wouldnecessarily be one of the conductors terminatin at the contacts formingthe set 282 of the switch 280 because, in such case, RA24I would remainin engagement with R0242, which contact is-connected to the switch wiper284.

At RA23I and R0233, the relay R230, upon operating, prepares animriulsing circuit extending to the' operating magnet 228 of the switch280. With the apparatus in this condition, the connector switchisconditioned to respond to the fourth and final digit dialed at thecalling substation A. At the beginning of the first impulse of thisdigit, the above-noted circuit for energizing the operating magnet 228is completed, this circuit extending from ground at RA20| by way ofR0203, RA208, R0209, the off-normal springs 259 and 259', RAM I, R02|2,RA2i5, the winding of R220, RA23I, R0233, and through the winding of themagnet 228 to battery. The resulting operation of the magnet 228 causesthe switch 280 to be conditioned to step the wipers 283 and 284 to thefirst off-normal position or into engagement with the first contacts of.their respective associated sets 28! and 282. When the relay R220operates, it completes, 'at RA22 i, the abovenoted path forshort-circuiting thearmature RA2I5 ofthe busy .relay R2 l4. At the endof the first impulse and when R200 restores to open the above-tracedoperating circuit for the magnet 228, the wipers 283 and 284 are steppedto the first off-normal position to select the two ringing conductorsterminating at the respective first contacts of the sets 28!. and 282.When this first step is taken by the wipers of the switch, the offnormalsprings 285 are moved to the oil-normal position. At the springs 285, acircuit, traced hereinafter, is prepared for energizing the releasemagnet 229 and, at the springs 281, a circuit is prepared for energizingthe busy relay R2l4, this latter circuit being traced hereinafter andbeing held open at the operated armature RA225 of the relay R220. Foreach succeeding impulse of the fourth digit dialed at the callingsubstation, the magnet 228 operates to cause the associated wipers 283and 284 to be stepped one step so that, at the conclusion of the digit,one of the wipers 283 and 284 will be standing in engagement with acontact terminating a ringing current" conductor having impressedthereon coded ringing voltage of the particular code which correspondsto the called substation E. As pointed out above, in the particular caseunder consideration and with R240 operated, the coded ringing currentmust be conducted to the called line 500 by way of one of the ringingcurrent conductors terminating at the contacts forming the set 28L If itbe assumed that the coded signal identifying the substation Ecorresponds to the code of the ringing voltage applied to the fourthconductor terminating at the contact set 28I, the final digit dialed atthe calling substation will necessarily comprise four impulses so that,at the conclusion of the digit, the wipers 283 and 284 will be leftstanding in engagement with their respective associated fourth contacts.

Shortly following the conclusion of the fourth digit dialed at thesubstation A, the relay R220 restores to open, at RA22I, a point in thepath short-circuiting the armature RA2|5 of the busy relay R2 l4 and tocomplete, at RA'225, the abovementioned circuit for energizing the busyrelay. This-circuit extends from ground at the lower one of theoff-normal springs 281 by way of the upper spring of this set, RA225,and through the winding of R2 to battery. The relay R2i4, uponoperating, opens, at RA2I5, a point in the circuit for energizing R220and the magnet 228 in series, thereby to prevent any further operationof the impulsing device provided at the calling substation fromeffecting further operation of the ringing code selecting switch 280. AtRA2I9,

R2l4 prepares a circuit for energizing R250,

which relay functions to complete a path for applying ringing voltage tothe talking conductors of the line extending to the called substation E.The .circuit for energizing R250 is completed when the ringinginterrupter switch is operated to a position to start a new ringingcycle, at which time a ground pulse is applied to CH5. Thus, if R2|4operates just prior to the operation of the wipers of the interrupterswitch into engagement with their respective associated first contacts,this circuit is completed when the wiper 315 is moved into engagementwith its associated first contact and extends from ground at the wiper315 by way of RA3I3, 0315, RA2I9', RA231, RA255, R0255 and through thelower winding of R250 to battery. The relay R250 now partially operatesto complete a closed circuit for shortcircuiting its upper winding, thiscircuit extending from ground as applied to the control conductor 0l24by way of RA254, the upper winding of R250, R0255, RA255, RA231 andRA2I9' back to ground on 03 l 5. When ground is subsequently removedfrom 03|5 through the movement of the wipers of the switch 300 out ofengagement with their respective associated first contacts, theabove-traced short-circuiting path is opened and the two windings ofR250 are energized in series, causing the relay R250 to complete itsoperation. Upon fully operating, R250 opens, at RA255 and R0255, a pointin the above-traced circuit for energizing its lower winding andprepares, at RA255 and RA255', a circuit for energizing the lowerwinding of R250. At RA| and RA252, a path is completed for projectingringing current over the conductors of the called line 500. In thepresent assumed case, wherein the code identifying the called substationE corresponds to that of the voltage applied to the ringing currentconductor 2!, the path of this current extends'from the upper terminalof the secondary winding 328 by way of R0333, RA332, the switch wiper 3"of the wiper 312, the conductor 2|, the wiper 283, R0243, RA24I, RA252,R0215, RA215, the wiper 245, the contact 245', the line conductor 050i,the condenser 504, the windings of the signal device 503, the switchsprings 52! and 528, 0502, the contact 245, the wiper 245;RA25I andRA21| to the grounded terminal of the secondary winding 328 at R0213. Itwill be understood that portions of this current are by-passed throughthe signal devices provided at each of the other stations associatedwith the line' 500. Due to the particular coding of the current,however, the subscriber at the substation E is in formed that hissubstation is being called and the other subscribers are informed thatthe call is not intended for their respective substations. A portion ofthe ringing current is by-passed by way of the condenser 210, RA253 andthrough the repeater windings 204 and 203 in series to ground at R0213to cause ring-back tone current to be impressed on the loop extending tothe calling subscriber's substation, thereby to indicate to the callingparty that the ringing operation is being performed. a

As indicated above,, one feature of the present invention pertains tothe arrangement of the apparatus whereby ringing current is only appliedto the called line for a predetermined number of the energization of itslower winding over a circuit extending from ground on C316 by way ofRA2I9', RA231, RA255, RC256', RA262, RC2, and through the lower windingof R260 to battery. With its lower winding energized over theabove-traced circuit, the relay R260 partially operates to complete, atRA26I, a closed circuit for short-circuiting its upper winding, thiscircuit extending from ground on the control conductor C124 by way ofRA26I, the upper winding of R260, RC204, RA262, RC256', RA255, RA231,and RA2 lilback to ground on C315. When ground is thereafter removedfrom CH5 through the continued operation of the interrupter switch 300,the above-traced short-circuiting path is interrupted and the relay R260fully operates to open, at RA262 and R0264, a point in the above-tracedcircuit for energizing its lower winding and to prepare, at RA262 andRC263, a circuit for energizing R210. This last-mentioned circuit iscompleted after the second ringing cycle is ended and at the beginningof the third ringing cycle when ground is again applied to the controlconductor C3 l 5. In this case, the circuit for energizing R210extends'from ground on C3l6'by way of RA2I9', RA231, RA256, R0256,RA262, R0263, RA210' and through the winding of R210 to battery. Whenenergized over the abovetraced circuit, R210 operates to complete, at

RA218, a holding circuit for itself, this circuit extending from groundas applied to C! by way of RA218 and the winding of R210 to battery. AtRA218, the relay R210 open-circuits the pickup or control lead C3l5,thereby to permit the ground pulses impressed on this lead to beeffective in controlling others of the connector switches in the groupincluding the switch illustrated in Fig. 2. The relay R210 opens, atRA21I and RA215 and their respective associated contacts R0213 andRC216, two points in theabovetraced path over which ringing current isprojected out over the called line 600 and also two points in the pathby way of which 'ring-back tone currents is impressed on the loopextending to the calling subscriber's substation. At RA21I and RA215 andtheir respective associated contacts R0214 and R6211, the conductors ofthe trunk line incoming to the connector switch are connected throughtothe conductor 060i and C602 of the called line, thereby to completethe.

connection to the called line. More particularly, the talking circuit iscompleted when the call is answered at the substation E. Thus, when thereceiver M5 is removed from its hook, the spring 62I is moved intoengagement with its associated contact springs 626 and 621 and thesprings 625 are closed. With the switch hook 620 in this position, thereceiver GIS is connected across the conductors of the line 600 and thetransmitter SM is included in a closed circuit by means of whichgenerated voice frequency currents may be impressed on the line 600through the transformer 6l0. In this connection, it is pointed out thatthe battery M3 is utilized in generating voice frequency currents at thecalled substation, whereas talking battery is supplied to the loopextending to the calling substation by way of the windings of the linerelay R200.

The release of a conection as established in the manner described aboveto the substation E is entirely under the control of the calling party.

Thus, if the receiver M5 is restored to its hook before the connectionis cleared out at the calling substation, the only result eflectedthereby is the disconnection of this receiver from across the conductorsof the line 600 and the inter- 5 ruption of the closed circuit includingthe transmitter 6. When, however, the calling party restores hisreceiver to its hook to open the loop circuit by way of which the linerelay R200 is held operated, this relay restores to open, at RA20I, theoperating circuit for the hold relay R204. When R204 restores, ground isremoved from the control conductor CI to cause the restoration of theselector switch I20 and the line switch I00 in the manner pointed outabove and to open the respective holding circuits for R260, R260, R260and R210. The relay R230, upon restoring, interrupts, at RA234, thepreviously traced circuit for energizing the cut-off relay R400, causingthe last mentioned relay to restore. When the hold relay restores, theabove-traced circuit for energizing the release magnet 269 is completed.The resulting operation of this magnet causes the wiper carriagestructure of the switching mechanism 246 to be restored to normal in themanner pointed out above, at which time the ofi-normal springs 265 arereturned to the normal position. When this occurs, the operating circuitfor the start relay R3l0 embodied in the control apparatus for theinterrupter switch 800 is opened and, assuming that none of the otherspecial connector switches are operated, this interrupter switch isrestored to normal in the manner pointed out above. When the hold relayR204 falls back, a circuit is also completed for energizing the releasemagnet 229 embodied in the code selector switch 200, this circuitextending from ground at RA20I by way of R0203, RA200, R6201, theoiT-normal springs 266 and through the winding of the magnet 229 tobattery. The resulting operation of this magnet causes the wipers oi theswitch 280 to be re- Operation of the apparatus to extend a connectionfrom a rural subscribers substation to an automatic subscriberssubstation Referring now more particularly to the operation of theapparatus to set up a connection between the line 600 and the line IN ona call originating at the substation E, the call is initiated throughthe operation of the magneto generator 606 provided at the callingsubstation. Before operating this generator, however, the calling partyshould listen in on the line to determine whether or not the line isbusy in connection with another call. This may be done by moving thehook latch 624 to a position for holding the contact springs 625 out ofengagement and thereafter removing the receiver 6l6 from its hook tocomplete a path-by way of which this receiver is connected across theconductors of the line 600. Specifically, this path extends from C60l byway of the impulsing springs 63L the transformer winding M2, thereceiver M5, the condenser 616, and the switch springs 621 and 62L Itwill be noted that this path is interrupted for direct current by thecondenser 1| '0". The purpose of inserting this condenser in the path isto prevent a short-circuit from being placed across the conductors ofthe line which might interfere with the dialing operation beingperformed at another of the substations associated with the line at thetime the line is challenged at the substation E. More particularly, thearrangement of the apparatus at each of the other stations is identicalwith that of the apparatus provided at the substation E, and it will beapparent that if the impulsing device at the last-mentioned station werebeing operated to deliver impulses to the switching equipment providedin the exchange and a short-circuit were placed across the conductors ofthe line 900, the

call would'either be falsely routed to the wrong substation or wouldfail entirely.

After the line is challenged and when the magneto generator 505 isoperated, alternating current is projected by way of the springs 908 andthe line conductors C50! and C502 through the upper winding of thealternating current relay R405, causing this relay to operate. Uponoperating, R405 completes, at RA'I, a circuit for energizing its lowerwinding in series with the start relay R520 provided in the commonequipment 500, this circuit extending from ground at the lower terminalof the winding of R520 by way of this winding, C522, RA402, RA40I, and

through the lower winding of R405 to battery.

At RAMS, the relay R405 opens a point in the path over which its upperwinding is energized and, at RA408, it completes a path for marking thecalling line 600 in the bank contacts of the finder switches to whichthis line extends. More particularly, battery is extended .through thewinding of R400 and by way of RA400 to the fifth contact of the contactset 494 in the finder switch 490 and to the corresponding contacts ofthe other finder switch banks.

The common equipment 500 operates in a manner such that the allotterswitch provided therein operates to a position corresponding to an idleone of the finder-repeater links immediately after an assigned link hasbeen caused to seize a calling line. Assuming, for example, that thewipers of this switch are standing in the position corresponding to thelink illustrated. that is, in engagement with their respectiveassociated tenth contacts, at the time the start relay R520 operates,this relay initiates the operation of the finder portion of the link tosearch for and seize the calling line 000. More particularly, when R520operates, it completes, at RA52I, a circuit for energizing the windingof R540 in series with the winding of the operating magnet 5, thiscircuit extending from ground at RA52I by way of the winding of R540,RA545, RA555, the armature H2 and through the winding of the magnet 5lltobattery. Due to the relatively high resistance of the winding of R540,the magnet 5 does not operate. Hence, the wipers of the allotter switchare maintained in the position corresponding to the link illustrated.The relay R540, however, operates to complete, at RA544, a circuit forenergizing the operating magnet 499 of the finder switch 490 and toprepare, at RA545, a circuit for energizing R530. At M5, the relay R540prepares a point in the holding circuit for R550 and, at RA543, itprepares a point, in the circuit for energizing the upper windings ofR550. At RA545, the relay R540 opens a point in the path normallyshort-circuiting theresistor 550 so that this resistor is included inthe series circuit over which the. relay R5 is held energized'.

The above-mentioned circuit over which the magnet 455 is energizedextends from ground at RA552 by way of R0554, RA544, RAIII, the wiper551, the tenth contact of the set 502, C524 and the winding of themagnet 400 to battery. When energized over this circuit, the magnet 400advances the wipers of the switch 400 one step and attracts its armature400' to complete the above-mentioned circuit for energizing R500, thiscircuit extending from ground at the contact associated with thearmature 400' by way of this armature, C525, the tenth contact of theset i, the wiper .500, RA545, and through-the winding of R550 tobattery. When R550 operates, it interrupts, at RA50I, the above-tracedcircuit for energizing the magnet 490, causing this magnet to restoreits armature 490' to interrupt the operating circuit for R555. When R530restores, it again completes, at RAI, the circuit for energizing themagnet 459, causing this magnet to operate to advance the wipers of theswitch 490 a second step and to again complete the operating circuit forR530. The interrelated operation of the magnet 490 and R530 continuesuntil such time as the wipers are moved to the position corresponding tothe calling line 500. Assuming that the movement of the wipers isstarted with these wipers occupying the position indicated in thedrawings, five steps on the part of the switch 400 will be requiredbefore these wipers .are moved into engagement with the contacts of theupper winding of the slow-to-release relay R550 in series with thewinding of R400, this circuit extending from ground at the lowerterminal of the upper winding of R550 by way of this winding, RA540, thewiper 500, the tenth contact of the set 505, C525 the wiper 490, thefifth contact of the set 494 RA405 and through the winding of R400 tobattery. When its upper winding is energized over the above-tracedcircuit, R550 operates to complete, at RA55I, a holding circuit foritself, this circuit extending from ground at RC542 by way of RA54I,RA55| and the lower winding of R550 to battery. At RA552 and R0550, therelay R550 opens a point in the above-traced operating circuit for themagnet 499, thereby to arrest the interrelated operation of this magnetand R500. At RA552 and R0553, the relay R550 completes a circuit forenergizing the switching relay R4l0, this circuit extending from groundat RA552 by way of R0550, the wiper 509, the tenth contact of the set504, C520 and through the winding of R4 to battery.

When R4|0 operates, it switches the subscribers loop circuit through tothe repeater portion of the link and completes. at RA4i4', a circuit forfully energizing the cut-oi! relay R400, this circuit extending fromground at RA4I4 by way of the wiper 490, the fifth contact of the set494,

to mark this line as busy in the bank contacts of the connector switchesto which it extends. I

At RA402, the relay R400 opens a point in the above-traced circuit forenergizing the lower winding of R405 and the start relay R520 in series,causing both of these relays to restore, assuming that none of the otherrural lines are waiting to be assigned finder-repeater links. If asecond calling line is waiting for a link at the time R400 operates, thestart relay R520 will be held energized and only R405 will restore. AtRAI, the relay R400 holds the upper winding of R405 disconnected fromacross the talking conductors of the line 600. Assuming that the startrelay R520 restores, it opens, at RA52I, a point in the above-tracedoperating circuit for R540, causing this latter relay to restore toopen, at RA54I, the holding circuit for R550. R550 restores, a point isopened in the abovetraced operating circuit for'R4I0. Before R550 fallsback, however, and during the sequence of operations just described,R560 is caused to operate to complete a holding circuit for R4I0.

Thus, immediately the subscriber's loop is extended to the repeaterportion of the link, a circult is completed for energizing the linerelay R4I5, this circuit extending from ground at the fifth contact ofthe set 492 by way of the wiper 496, RA4I3, the repeater winding 414,RA4I4, the switch wiper 491, the fifth contact of the set 493, 060I, theimpulsing springs 63I, the transcontact of the set 49I, the wiper 495,RA4I2, the

' repeater winding 413, and through the winding of R4I5 to battery. Therelay R4I5 operates,

ground at RA42 I, by way of R0422 and the winding of R430 to battery. AtRA424, the relay R420 completes a holding circuit extending by wa f th r424 mint inin 't If.

y 0 e eslstor for a a g 1 Se R460 is operative to connect the conductorsof operated independently of the hold relay R430. When thelast-mentioned relay operates, it opens, at RA43I and R0432, a point inthe above-traced operating circuit for R420, prepares, at RA434, a pointin the circuit, traced hereinafter, for en-.

ergizing R450, and completes, at RA435, a circuit for energizing R560,which latter circuit extends from ground at RA435 by way of RA58-I andthe upper winding of R560 to battery. When R560 operates, it completesthe above-noted-holding circuit for-R4I0, this circuit extending from'ground at RA56I by way of R0563, 0526 and the winding of R4I0 tobattery. As indicated above, the arrangement of the apparatus is suchthat this holding circuit is completed through the operation of R560before R550 restores to open the operating circuit for R4I0. When R560opermark the finder-repeater link illustrated as busy in the allotterswitch provided in the common equipment 500.

In the event the start relay R520 remains oprelays R540 and R550 areheld operated until R560 operates. When the last-mentioned relayoperates. the winding of R540 is short-circuited at RA565, causing R540to restore to open, at RA54I, the holding circuit for R550. When R550restores, it completes a circuit for energizing the operating magnet 5of the allotter switch, this circuit extending from ground at RA565 byway of the wiper 5I0, RA546, RA555, the circuit-interrupting contactsassociated with the armature 5I2, and the winding of the magnet 5 tobattery. The magnet 5, upon being energized over this circuit, attractsits armature to open its operating circuit and to step the wipers of theallotter switch one step or into engagement with the contacts of the setcorresponding to the next finder-repeater link. If this next link isbusy, the contact of 'the set 505 which corresponds thereto will alsohave ground potential impressed thereon so that the magnet 5II such timeas the wiper 5I0 encounters a contact.

corresponding to an idle one of the finder-repeater links, th'is idlecondition being indicated by the absence of.ground potential on thecontact corresponding thereto. Thus, when the link illus-' trated isidle, R560 is deenergized so that the tenth contact is open-circuited.When, therefore, the allotter switchis operated to a positioncorresponding toan idle link, no further circuit is available forenergizing the magnet 5I I, and the stepping operation of the switch isarrested.

Following the operation of R4I5, R420, R430 and R560, the controlapparatus embodied in the repeater portion of the link is conditionedto" respond to the first series ofimpulses dialed at the substation E.

As pointed out in the introductory portion of the specification, thearrangement of the repeater portion of each link is such that apreliminary or prefix digit is required to cause a loop circuit to beestablished between the repeater portion of the link and its associatedline switch. More particularly, with the link illustrated, the relay thetrunk line I25 across the secondary windings of the repeater coil 412only following the dialing of a digit comprising ten impulses at acalling substation on a line tu which the link has been allotted foruse. An impulse correcting relay network is provided such that thecharacter of each impulse repeated over the trunk line I25 is, withinlimits, independent of the character of the corresponding impulse dialedat the calling substation. I At the beginning of the first impulsedialed at the calling substation E, the abovetraced loop circuit overwhich R4I5 is energized is interrupted at the impulsing springs 63 I.During impulsing, the shunt springs 632 of the impulsing device 630 aremoved to the oif-normal position to short-circuit the receiver 6| 5 inseries with the secondary winding 6I2 of the transformer 6I0. ,When R4I5restores in response to the interruption of the above-traced loopcircuit, it opens, at RA4I9, the circuit over which R420 is heldenergized and completes, at RA4I6 and R04", a priming circuit 'foritself, this latter circuit extending from ground at RA43I by way ofR0433, RAMS, RC4", the resistor 4H and the winding of R4I5 to' battery.When R420 restores, it opens, at RA424, its holding circuit andcompletes, at RA42I, a circuit for energizing 1 3 erated following theoperation of R400, the two the lower winding of R450, which circuitextends from ground at RA42I by way of R0423, RA454, RA444 and the lowerwinding of R450 to battery. The relay R450, upon operating,short-circuits, at RA452, its upper. winding, thereby to render itselfslow-to-release, and completes, at RA45I, an obvious multiple holdingcircuit for the hold relay R430. At RA454, the relay R450 completes acircuit for energizing the lower winding of R440, this circuit extendingfrom ground at R0454 by way of RA454, the resistor 450, RA425, andthrough the lower winding of R440 to battery. With R440 deenergized, itsupper winding is short-circuited at RA4 3 and, hence, this relaypossesses a slow-to-operate, characteristic. It operates, after aninterval, however, to open, at RA443, the path short-circuiting itsupper windingwhereby it is rendered fast-to-release. At RA444, the relayR440 opens the operating circuit for R450. With R440 operated, and whenthe line relay R4I5 reoperates at the end of the first pulse, a circuitis completed for again energizing R420, this circuit extending fromground at R0442 by way of RA44I, RA4I9 and through the winding of R420to battery. The relay R420 now reoperates to complete, at RA424, itsabovetraced holding circuit and to open, at RA425, the operating circuitfor R440, causing this latter relay to restore. The restoration of R440does not result in the recompletion of the operating circuit for R450,however, since this circuit is now open at RA42I and RC425. Theabovedescribed cycle of operation and restoration of the relays R4I5,R420, R450 and R440 is repeated for each impulse dialed at the callingsubstation E. Since, in the present assumed case, the preliminary digitdialed at the substation E comprises ten impulses, it will be understoodthat, during this digit, the cycle of operation of the relays noted isrepeated ten times. As indicated previously, R450 is the impulsingrelay, and it will be apparent from the foregoingdescription that therelation between the period of deenergization and the period ofenergization of this relay during each impulse is, within limits,independent of the relation between the corresponding periods for theline relay R4I5. More particularly, the restoration of R4I5 at thebeginning of each impulse cycle initiates the operation of the threerelays R420, R450 and R440 to repeat the impulse, and the extent of theperiod during which R450 is energized depends primarily upon theslow-to-release characteristic of this relay and the slow-to-operatecharacteristic of R440.

During the period of each impulse when the pulsing relay R450 isoperated, a circuit is completed for energizing the slow-to-releaserelay R415 and the operating magnet 485 of the switch 480 in parallel,this circuit extending from ground at RA453 by way of RA464 to RA41I,where it divides, one branch extending through the winding of R015 tobattery and the other branch extending through the winding of the magnet485 to battery. The relay R415 operates at the beginning of the firstimpulse repeated by R450 and remains operated during the'succeedingimpulses and until the digit is completed. At its armature :RA-i'lt,this relay opens a point in the circuit, traced hereinafter, forenergizing-R410. Obviously, at the end of the first and each succeedingimpulse, the above-traced circuit for energizing the magnet 005 isopened. Each time this magnet is deenergized following its energization,it steps the wipers 403 and 404 one step. Since the preliminary digitcomprises ten impulses, the wipers noted will be stepped to the tenthof!- normal position or into engagement with their respective associatedtenth contacts. At the beginning oi the first step taken by the wipersof the switch 400, the oil-normal springs 400 are closed to prepare acircuit for energizing the release magnet 401. This circuit is held openfor the duration of the call, however, through the continuedenergization of R500.

If it be assumed that the wipers of the switch 400 are successfullyoperated into engagement with their respective associated tenth contactsin response to the dialing of the preliminary digit at the callingsubstation E, shortly following the restoration of R450 at theconclusion of the digit, the relay R415 restores, but without effect.Immediately the wiper 400 is moved into engagement with the tenthcontact of the set I, a circuit is completed for energizing R400, thiscircuit extending from ground at the wiper 400 by way of its associatedtenth contact and the winding of R400 to battery, This relay, uponoperating, opens, at RA404, a point in the above-traced circuit forenergizing the magnet 405 and the relay R415 in accordance with theoperation of the pulsing relay R450. At RA450, the relay R400 completesan alternative holding circuit for R500, this circuit extending fromground at RA435 by way of RA400 and the upper winding of R500 tobattery. At RA405, the relay R400 opens a point in the holding circuitfor R510 and the initial holding circuit for R500. Through thisoperation, the link release relay R500 is prevented from operating toinitiate the release of the link in the manner pointed out more indetail hereinafter. At RAI and R0402, the relay R400 opens a point inthe path, described hereinafter, for connecting the artificial leakimpedance element 4| I' across the conductors of the line 000.

When the relay R400 operates, it also completes a loop circuit to theline switch I50 terminating the trunk line I25. More particularly, thisrelay connects a bridge across the line conductors of the trunk I25,this bridge extending from the trunk line conductor CI20 by way ofR0401, RA400, RA455, the repeater winding 410, the resistor 450, therepeater winding 410 and RA403 to the opposite trunk line conductor CI21. When this loop circuit is completed, the line switch I30 operates inthe usual manner to extend the connection to an idle one of the selectorswitches. Assuming, for example, that the selector switch I40 is thefirst idle switch available, when the loop cir'cuit is extended theretothrough the operation of the line switch I30, it is conditioned torespond to the second series of impulses dialed at the callingsubstation E.

During the dialing of the second digit at the calling substation, thefour relays R4I5, R420, R450 and R440 respond in the exact mannerpointed out in detail above; that is, R450 operates once during eachimpulse. Each time R450 operates, it opens, at RA455, the loop circuitas extended to the selected selector switch I40, which selector switchresponds to the repeated impulses by elevating its wipers in the usualmanner to a position opposite the level of bank contacts terminating thetrunk lines extending to the connector switches having access tothecalled line I.0I. Thereafter, the selector switch operates automaticallyto select an idle one of the connector switches in the selected group.Assuming that the connector switch I50 is the first available switch inthe selected group, when the wipers of the selector switch I40 are movedinto engagement with the contacts terminating the trunk line extendingto this connector switch, the loop circuit is, automatically extended tothe last-mentioned switch, causing this switch to be conditioned torespond to the impulses making up the third and four digits dialed atthe calling substation E. When the third digit is dialed at the callingsubstation, the connector switch I50 responds to select the group of tenlines including the called line IOI, it being again pointed out that theimpulses of this digit are repeated to the operated connector switch I50through the interrelated operation of the relays R4I5, R420, R450 andR440. Following the selection of the ten-line subgroup, and when thefourth digit is dialed at the substation E, the connector switch I50operates to select the called line. IOI. In order to insure a faithfulresponse of the seized switches I40 and I50, or of other switchesrespectively corresponding thereto,

to the operation of thepulsing relay R450, all such I nector switch I50functions to test the called line to determine its idle or busycondition, to return busy tone over the established loop to the callingsubstation in case the called line is busy at the time it is selected,and to apply ringing current to the, called line in case the line isidle, is identical to that described above with reference to theconnection established between the substations A and B on a callinitiated at the substation A. Assuming that the called line is idle atthe time it is selected by the switch I50, the desired conversationalcircuit is completed when the call is answered at the called substationA.

The release of the operated switches I50, I40 and I30 and of theoperatedfinder repeater link is preferably solely under the control of thecalling party. Thus, when the "calling party restores the receiver 6I5to its hook to return the springs of the hook switch 620 to normal, theloop circuit over which R4I5 is held energized is interrupted at thesprings 62I and 621. When R4I5 restores, it opens, at RA4 I 9, thecircuit over which R420 is held energized. The last-mentioned-relay nowrestores to open, at RA42I and RC42-2, the operating circuit for thehold relay R430. This hold relay, upon restoring, opens, at RA435, thehold circuit for R560. When R560 restores, it removes,

at RA565, ground from the contact of the set 505 corresponding to thefinder-repeater link illustrated, therebyv to mark this link as idle inthe bank contacts of the allotter switch; When R560 restores, it alsocompletes a circuit for energizing the release magnet 481, this circuitextending interrupt the operating circuit for the magnet 081. When,during the restoration of the switch 480, the wiper 483 is moved fromengagement with the tenth contact of the set 48I, the circuit over whichR460 is held energized is interrupted, causing this relay to restore toopen, at RA463 and RA466, the loop circuit which extends reference to acall initiated at the substation A and extended to the substation B.

When B560 restores, it further functions to open, at RA56I and R0563,the holding circuit for R4I0, causing this relay to restore to remove,at RA4I4', ground from the control conductor C603 of the line 600. Theremoval of ground from the control conductor noted results in therestoration of R400 and, when this relay restores, it reconnects theupper winding of R405 across the line conductors of the line 600 andreprepares the start circuit for energizing the lower winding of R405 inseries with the start relay R520. The apparatus is now completelyrestored to normal and in readiness for further use. In this connectionit is pointed out that the finder portion of the link is of thenon-homing type; that is, the wipers of the switch 490 remain in theposition to which they are operated during a line hunting operationuntil further operation .of the switch is initiated.

As pointed out in the introductory portion of the specification, one ofthe features of thepresent invention is concerned with the arrangementof the apparatus whereby a calling rural subscribers line can only gainaccess to the regular automatic switching equipment provided in theautomatic exchange through a predetermined operation of the dialingdevice at the calling substation on the calling line to transmit apredetermined series of impulses to a seized finder-connector link. Itmay happen that, due to a faulty condition of the line, the line relayincluded in the finder-repeater link operatively associated with thecalling line will not respond to all of the impulses dialed at thecalling substation, but only to a portion thereof. On the other hand,the calling party may, through carelessness, fail to dial the requisitenumber of impulses. Obviously, in either case, a false call would resultif the impulses were dialed directly into one of the automatic switchesin-,,

cluded in the regular automatic switching equip--" of the regularswitching equipment is tied up due to eithe'rof the two causes noted.Moreover, the arrangement is such that the impulsing conditions of anycalling line are tested when the control apparatus of the-associatedfinder-repeater link is responding to the impulses of the prefix digitdialed at the calling substation. This test is achieved by connecting aleak impedance across the conductors of the calling line during thetransmission of the impulses making up the prefix digit, therebyartificially to reduce the impulse transmitting efficiency of thecalling line. If the line relay of the operated finder-repeater linkfaithfully responds to the impulses of the preliminary digit under theadverse impulsing conditions imposed by the leak impedance, thisimpedance is disconnected from across the line conductors during furtheroperation of the dialing device at the calling substation, thereby toin-' crease the impulse transmitting efliciency of the line. Thus,considering again the operation of the link illustrated to extend aconnection from the substation E to the substation A on a call initiatedat the first-mentioned substation, when the relay R4I0 operates toextend the subscriber's loop circuit through to the repeater portion ofthe link illustrated in Fig. 4, it not only completes the above-tracedcircuit including the conductors of the line 600 for energizing the linerelay R4I5, but connects the resistor 4| I in series with the tworepeater windings 413 and 414 across the

